This invention relates to thickening agents containing water-dispersible polymers which agents are used to increase the viscosity of aqueous media.
U.S. Pat. No. 4432881 discloses a thickening agent which comprises a water-soluble polymer having pendant hydrophobic groups and a water-dispersible surfactant having hydrophobic groups that are capable of associating with the hydrophobic groups of the polymer. The patentee indicates that the relative proportions of the two components of the thickening agent are such that, when the thickening agent is dispersed in water in a concentration of 0.5 weight percent based on the water, the viscosity of the water is at least doubled, the thickening agent being such that the water can be subjected to mechanical shear without significant loss of viscosity. Additionally, the thickening agents are said to be such that their viscosity is not reduced by the presence of electrolytes such as sodium chloride etc.
The copolymers disclosed as useful in the above-mentioned patent for the production of the thickening agents thereof comprise a copolymer of a water-soluble monomer such as acrylamide and a hydrophobic group-containing comonomer such as dodecyl acrylate or methacrylate. The patentee indicates that such copolymers, when used in conjunction with a hydrophobic group containing surfactant, result in thickening agents which increase the viscosity of water when added thereto.
The use of the surfactants has been found to be unnecessary by Applicants in that their necessity has been shown to be obviated by the use of a third monomer, i.e, a water-soluble monomer which when copolymerized with the other two monomers results in the formation of a water-soluble terpolymer. It was discovered that the copolymers of U.S. 4432881, when produced at certain high molecular weights, are water-insoluble as such and do not function as described therein even when a surfactant is present in amounts specified. Thus, the copolymers of said patent are actually limited to those having molecular weights such that they are water-soluble.
Applicants have discovered that useful thickening agents containing polymers having very high molecular weights, i.e, up to about 10 million can be produced in the absence of the surfactant indicated as essential by the patentees of U.S. 4432881. Thus, thickening agents containing polymers having very high molecular weights can be utilized, which polymers, when produced according to U.S. 4432881, do not function as described therein. The agents exhibit thermal stability, electrolytic tolerance and good resistance to shear.